Because it was one of the first books written in Italian rather then Latin, seeing as which Latin was the dominant way of text writing for the Italian states.Which is why he is often called the father of the Italian language. Not only that, Dante Alighieri (One of my favorite authors) wrote it for the intention for people to become enlightened to themselves, notice that the sins they commit have a dire consequence to them. So placed in Dante's first book that started it all, the Inferno. Dante stated that, while he was in the Second Circle,
"I reached a place where every light is muted, which bellows like the sea beneath a tempest, when it is battered by opposing winds. The hellish hurricane, which never rests, drives on the spirits with it's violence: wheeling and pounding, it harasses them. When they come up against the ruined slope, then there are cries and wailing and lament, and there they curse the force of the divine. I learned that those who undergo this torment are damned because they sinned within the flesh, subjecting reason to the rule of lust. (Canto V, 28-39)"
He basically stated that if you live your life with the sin of lust, you are forever condemned to spend eternity trapped in a hurricane like whirlwind, spinning and thrashing against the others who are also subjugated there. Could you imagine if you read that during this time and you were a die-heart catholic in Italy?! This would make anyone change to not suffer there, and there is plenty more like the punishments for Wrath, Gluttony, Heresy, etc.